Volume 108, Issue 4

Al–Ti alloy films with various Ti contents were prepared through magnetron co-sputtering with Al and Ti targets and treated with vacuum annealing at 400 °C. Energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and nanoindentation were used to determine the composition, microstructure and hardness of the films to reveal the existence of intermetallic compounds and their effects on the microstructure and mechanical properties. The results showed that Al–Ti films with lower Ti contents formed nanocrystalline structures of highly supersaturated solid solution. With the increase of Ti content, various types of Al–Ti intermetallic compound bonds formed. The existence and increasing concentration of these compound bonds gradually transformed the films into amorphous structures and supported the continual increase of the film hardness, reaching a high value of 8.8 GPa at 36.3 at.% Ti.

In petroleum drilling engineering, materials with high strength and rapid degradation are required for degradable fracturing ball applications. In this work, the microstructure, mechanical properties, and corrosion behavior of extruded Mg-3Zn-Y- x Cu ( x = 0, 1, 3, 5 weight percent) alloys are investigated using optical microscopy, scanning electronic microscopy equipped with energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electronic microscopy, compression tests, electrochemical measurements, and hydrogen evolution tests, to explore their potential as excellent candidate alloys for degradable fracturing ball applications. It is found that the Mg-3Zn-Y alloy is mainly composed of α-Mg, Mg 3 Zn 3 Y 2 , and Mg 3 Zn 6 Y phases. After Cu addition, a new MgZnCu phase is formed, while the Mg 3 Zn 3 Y 2 phase disappears. The Mg-3Zn-Y-3Cu alloy shows the highest compressive strength (473 MPa) and yield strength (402 MPa), mainly attributed to the combined effect of the fine-grain and dispersed precipitation of Mg 3 Zn 6 Y and MgZnCu. The corrosion rate of Mg-3Zn-Y-3Cu reaches 0.41 mm day −1 in 3.5 wt.% KCl solution. Consequently, Mg-3Zn-Y-3Cu alloy is a suitable degradable fracturing ball-seat material.

The effects of pouring temperature, the content of a rare earth ( RE ) metal modifier, and T6 heat treatment on the microstructure and mechanical properties of Al-25 % Si alloy were investigated. The results show that for the unmodified alloy, the morphology of primary Si was transformed from coarse polygons and platelets to fine polyhedral, and the average size decreased with increasing pouring temperature. The primary Si exhibited a small blocky morphology with an average size of 47 μm at an optimal content of 1.2 % RE . The tensile strength and elongation were enhanced by the addition of RE followed by the T6 heat treatment, and the maximum tensile strength and elongation (208.3 MPa and 1.01 %) were obtained for the sample modified with 1.2 % RE followed by the T6 heat treatment.

The effects of temperature and strain rate on the tensile properties of Timetal 834 near-α titanium alloy and alloy 834 without silicon were examined in the temperature range of 250 °C to 600 °C, employing strain rates in the range of 6.67 × 10 −6 s −1 to 6.67 × 10 −3 s −1 . Manifestations of dynamic strain aging such as serrated flow, plateaus in the variations of 0.2 % yield strength and ultimate tensile strength, peak in strain hardening exponent with temperature and negative strain rate sensitivity were observed in both the alloys. Serration maps in terms of strain rate versus temperature are presented for both the alloys. The activation energy for serrated flow was determined in both the alloys by employing various methodologies mentioned in the literature. Analysis of the results suggested that addition of Si leads to increased severity of dynamic strain aging.

This paper presents the results of studies on the effects of thermal treatment on the structure, hardness and strength of a high-aluminium monotectoid ZnAl40Cu3 alloy. The alloy was tested in the following conditions: after supersaturation at a temperature of 385 °C; after supersaturation at a temperature of 385 °C and subsequent ageing at temperatures of 125, 150 and 175 °C; and after annealing at a temperature of 185 °C. The studies revealed that annealing at a temperature of 185 °C causes a decrease in hardness and strength of ZnAl40Cu3 alloy. In contrast, the highest increase in hardness and strength was obtained by “incomplete” supersaturation at a temperature of 385 °C for 10 h. The increase in hardness and strength of the ZnAl40Cu3 alloy observed in the result of “incomplete” supersaturation at a temperature of 385 °C for 10 h may be connected with, most of all, formation of a quasi-dendritic structure. It was found that ageing of supersaturated samples causes a decrease in their hardness when compared to that of the samples after supersaturation.

The effect of plastic deformation on the properties and microstructure of W–Cu composites produced by multi-pass hot extrusion with steel cup was investigated. W–Cu composites were sintered at 1 100 °C and then the sintered billets were firstly extruded at 900 °C with different extrusion ratios. The second hot extrusion was performed at 900 °C. The plastic deformation of copper phase plays a dominant part during the whole extrusion process. The microstructural evolution of W phase during the whole processing of heavy hot deformation can be divided into different stages. Experimental results indicate that the W agglomeration will be broken into fine particles effectively when the accumulated plastic deformation amounts to 97.6 % after the second extrusion.

CuBi 2 O 4 nanoparticles were prepared via a polyacrylamide gel route. Field-emission scanning electron microscopy observation shows that the particles are shaped like spheres and have an average particle size of ∼230 nm. Ultraviolet–visible diffuse reflectance spectroscopy reveals that the particles have a bandgap energy of 1.88 eV. The electrochemical performance of the sample was investigated by means of cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy in 2 M KOH, 6 M KOH, and 2 M NaOH electrolytes at different temperatures. It is demonstrated that the temperature has an important effect on the electrochemical performance of the sample, and relatively higher specific capacitance is observed at 45 °C, reaching 1 458 F g −1 in 2 M KOH electrolyte at a current density of 2 A g −1 . In addition, the sample exhibits an increased capacitance in a higher-concentration electrolyte, but its charge–discharge cycling stability is decreased. Moreover, it is found that the sample exhibits relatively larger specific capacitance in KOH electrolyte than in NaOH electrolyte.

Three dimensional (3D) glass fiber epoxy composites reinforced with nano-SiO 2 particles at ratios of 0.5 wt.%, 1 wt.%, 2 wt.% and 3 wt.%, were manufactured using the vacuum infusion method to improve the mechanical properties. Differential scanning calorimetry, thermo-gravimetric analysis, particle dispersion detection by color measurement, scanning electron microscopy, energy dispersive X-ray spectroscopy mapping, three point bending and tensile testing were performed to characterize the nano-particle-reinforced 3D composites. Mapping and color measurement revealed good dispersion of the nano-particles. The mechanical tests showed improvement rates of 52 % and 64 % respectively on warp and weft directions compared with the non-reinforced 3D composite. The tensile strength of the nano-SiO 2 reinforced 3D woven composites also increased to 6 % and 10 % according to the warp and weft directions compared with the non-reinforced 3D composite.

A comparative study of unary and binary carbon nanofiller reinforced high density polyethylene (HDPE) composites with 4 wt.% nanofillers was carried out in order to assess the reinforcement effect and synergy of carbon nanofillers with different dimensions. Rheology and resistivity tests indicate that the relative effectiveness of generating rheological and conductive networks is as follows: multi-walled carbon nanotubes (MWCNTs) > carbon black (CB) > graphene nanoplatelets (GNPs), while the reinforcement effect in modulus is: GNPs > MWCNTs > CB, at the same loading. The resistivity of all the HDPE/CB/MWCNT composites is quite close to the that of HDPE/MWCNT composites, indicating CB may be a good replacement for MWCNTs considering the relatively low cost of CB. A synergistic effect in modulus is observed in the HDPE/GNP/MWCNT and HDPE/CB/MWCNT composites due to the formation of nanofiller–polymer–nanofiller network structures.

The borothermal reduction of metal oxides in molten salts is reported as a general method towards transition metal monoboride nanopowders. Crystallized CrB powders with average particle sizes of 40 – 50 nm were synthesized at a lowest temperature of 800 °C. The presence of molten salts greatly inhibited the formation of impurities and the grain growth of CrB particles. NbB and TaB powders were also successfully synthesized by the same method at 1 000 °C and 1 100 °C, respectively.